The objective of this proposal is to quantitate atheromatous plaque volume in major epicardial coronary arteries by minimally invasive means. This objective is motivated by the need to make presymptomatic detection of coronary artery stenoses and the need to monitor the progression, or regression, of atheromatous plaques over a period of time. We propose to use the Dynamic Spatial Reconstructor (DSR), a fast multislice x-ray CT scanner that has recently been modified to permit quantitation of 25-50% stenoses in a 2mm diameter coronary artery using a central venous bolus injection of contrast medium. In the current proposal we request funds to upgrade the Charge Coupled Device (CCD) television camera based x-ray image chains on the DSR from the current analog mode of operation to all digital, 'on gantry', operation so as to provide the increased resolution needed for the technically more demanding task of this proposal. We propose to use the Biosound 12mHz sector scanner intraoperatively immediately after onset of cardioplegia, just prior to commencing revascularization, to provide the true volume of plaque from several cross section images along the left anterior descending coronary artery in the region of the selected stenosis. The value would be compared to the volume of plaque computed from the presurgical DSR scan. The DSR scan would be performed on all consenting patients selected for coronary bypass surgery on the basis of their clinically indicated coronary arteriogram. Past DSR studies of dogs have shown that the volume of hollow cylindrical plastic plugs introduced into coronary arteries could be quantitated over a range from 5mm3 to 25mm3, with a standard error of the estimate of 2mm3. These cylinders were approximately 2mm long and 2-3mm outside diameter, resulting in 50-80% stenoses of the vessel lumen. This method, if successful, would in conjunction with the other demonstrated capabilities of the DSR images, provide quantitation of the presence and severity of a coronary stenosis, the volume of the plaque causing the stenosis and the impact on myocardial perfusion distal to the stenosis; all from a single central venous injection of contrast agent.